The disorders of peroxisome biogenesis (PBD) which include Zellweger syndrome, infantile Refsum, and neonatal adrenoleukodystrophy result in mental retardation, retinitis pigmentosa, and lead to early death. Docosahexaenoic acid (DHA) is a key component of retina and brain. It has been demonstrated that peroxisomal synthesis of DHA and plasma levels are greatly diminished in PBD. Martinez et al (Neurology 1993;43:1389-97) increased plasma levels by supplementation with DHA ethyl ester and this resulted in clinical improvement in one child. We and others have demonstrated that plasma levels could be raised with the oral administration of DHA. The aim of the study is to test if the supplementation of DHA can alter the clinical course specifically improve the visual and neurologic function affected in these disorders. The study is a double-blinded, randomized, placebo-controlled study. It is planned to enroll 60 patients. Children with PBD are evaluated at baseline with neurologic assessment, neuropsychologic measures, and ophthalmologic studies including electroretinogram and visual evoked potentials. They are then assigned to treatment or placebo. Treatment is a microencapsulated form of DHA that is taken orally at a dose of approximately 100 mg/kg/day. This preparation can be mixed with food and is well tolerated. The placebo is a mixture of vegetable oil prepared in a similar fashion to the DHA preparation. Children return in one year and undergo repeat evaluation using the same battery.